This application is based upon application No. 11-276442 filed in Japan, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a spatial modulation unit, a luminous flux deflection device, a focus detection device, a camera and a focus control device, which are capable of changing the focal position.
2. Description of the Related Arts
Conventionally, there have been known a plastic mold Fresnel plate, a photographic dry plate type diffraction grating, a glass plate marking-off type diffraction grating, a photographic dry plate type hologram and a photoresist type hologram, in each of which the transmission or reflection optical path is fixed in the manufacturing stage.
As a technique for deflecting the transmission or reflection optical path, there are, for example, the following techniques.
In Japanese Non-examined Laid-open Patent Publication No. 10-62609, there is disclosed a microlens capable of adjusting the focal position. The microlens is constituted by a single lens by itself, can change the focal position thereof and is applicable only to a lens with a small-diameter pupil. If the microlens is simply increased in dimension, then the necessary spherical surface (aspherical surface) cannot be obtained, meaning that the practicality is presumably difficult. The disclosed microlens is intended to constitute an image-forming optical system of an imaging device and has neither effect nor construction for preventing the pupil shading caused by the imaging lens.
In Japanese Non-examined Laid-open Patent Publication No. 9-184965, there is disclosed a technique for providing the deflector for deflecting the incident optical path with a power. However, the lens power is not changed, and the pupil of the imaging lens cannot be effectively used.
Also, a technique capable of forming a microlens array and changing the focal position has been known. However, only a lens having a diameter of several tens to several hundreds of micrometers can be formed.
For example, FIGS. 18 and 19 show a conventional liquid crystal cell. There are proposed a prism element capable of varying the deflection angle and a lens capable of varying the focal position, by using liquid crystals that exhibit an anisotropic electrooptical characteristics. Namely, the molecular alignment state of liquid crystals are controlled.
FIG. 18 is a view of a liquid crystal cell constructed of nematic liquid crystals 401. The reference numerals 410 and 411 denote circular hole pattern electrodes, across which a voltage V is applied. An equipotential surface in this case is indicated by the wavy lines in FIG. 18.
Then, a plurality of cells of FIG. 18 are assembled to form the structure of FIG. 19. The structure includes a liquid crystal layer 401 for generating a refraction power, alignment films 404 and 405 and glass substrates 402 and 403. The reason why the alignment films are coated is to align the liquid crystal molecules in one direction by performing a rubbing process. Holes 410a and 411a of the circular hole pattern electrodes 410 and 411 become the respective lenses.
If a voltage not lower than the threshold value is applied to the liquid crystal cell, then there is obtained a liquid crystal alignment state determined depending on the alignment regulation force of the substrate, the elasticity force of the liquid crystals and the alignment force caused by the electric field. This state is shown in FIG. 18. The inclination of alignment varies depending on the distance from each electrode. The refractive index is small near the electrodes, and the refractive index is great at the center of the circular hole. With this arrangement, a characteristic similar to that of a convex lens can be obtained.
Conventionally, one cell has a diameter size of 300 xcexcm and a liquid crystal thickness of 100 xcexcm, and the application voltage has about 1 to 5 V. The effective region has a very small region and is intended, for example, for condensing the laser light beam to about 2 xcexcm. Namely, it is impossible to use the effective region in a size that can be expressed on the order of millimeters.
Also, a diffraction grating capable of changing the optical path is known. However, this is not constructed by itself so as to have a focal position.
Also, a display device whose optical path is changed by a micro-mirror is known. This device is intended to spread a point light source into a wide range for display and is not constructed only by itself so as to obtain a focus. If it is tried to obtain a focus by this device, then unevenness will presumably result in since the arrangement is a square arrangement.
With regard to an incident luminous flux deflecting device to be utilized for a sensing device for sensing the focus of an optical device or the like, the following techniques have conventionally been known.
For example, in Japanese Non-examined Laid-open Patent Publication No. 10-62681, there is disclosed a technique for varying a shielding means by the open f value of the imaging lens inside the sensing unit. However, the lens power is not changed, and the position of the shielding portion moves (baseline length is varied) to disadvantageously change the sensing accuracy.
In Japanese Non-examined Laid-open Patent Publication No. 58-78101, there is disclosed a technique for setting the power of the field lens arranged in the vicinity of the focal plane of the imaging lens so that the image of the image-forming lens falls within the exit pupil. However, there is achieved no change according to the pupil position and diameter of the imaging lens.
In Japanese Non-examined Laid-open Utility Model Publication No. 55-155223, there is disclosed a technique for changing a shielding means symmetrical about the optical axis inside the sensing unit according to the mounting/dismounting of the focalplane plate. However, the lens power is not changed, and the shielding portion is moved. Furthermore, the necessary quantity of light cannot be obtained.
As described above, in the Japanese Non-examined Laid-open Patent Publication No. 9-184965, there is disclosed a technique for providing a deflection means for deflecting the incident optical path with a power. However, the lens power is not changed, and the pupil of the imaging lens cannot be effectively used.
When executing a sensing operation for the purpose of imaging and measurement by utilizing the luminous flux from the subject, which has been incident on the object lens and passed through the pupil of the object lens, in general, the luminous flux should preferably be utilized within the full span of the exit pupil of the lens taking the sensing range (area) and accuracy into consideration.
However, when executing a focus detecting operation by means of, for example, a camera, then the position and size of the exit pupil differs depending on the type of the imaging lens, or the object lens, and the pupil position and size are changed by focusing and zooming even with an identical imaging lens. Conventionally, the optical path is fixed, and therefore, the optical path is designed according to the type of the imaging lens and the possible minimum size of the exit pupil when focusing or zooming operation is executed. Based upon the above reasons, there have been limitations on an improvement in accuracy and on the widening of the focus area using an area sensor.
Namely, with regard to the focus detection accuracy, a higher accuracy can be obtained when a wider exit pupil region is used. The accuracy is determined depending on the distance between the two rays of luminous flux that form the two subject images from the optical axis of the imaging lens. The greater the distance between the rays of luminous flux in the exit pupil position, the higher the accuracy is. If the focus detection area is set wide, then the center of the luminous flux comes closer to the optical axis due to the wideness of the area. In order to increase the accuracy and widen the area, it is important that the exit pupil should be wide, and it is required to effectively utilize the exit pupil as wide as possible in terms of design.
It has conventionally been impossible to replace the AF module in correspondence with the type or state of each lens. Therefore, the AF module has been designed in accordance with the lens of the minimum exit pupil among the lenses to be used. That is, even with an imaging lens capable of detecting the focus with high accuracy or with a lens capable of detecting the focus in a wide area, the focus detecting operation is executed with the accuracy and the area range according to a lens in undesirable conditions.
Accordingly, it is an object of the present invention to provide a focus detection device that can efficiently utilize the luminous flux that has passed through the exit pupil of an object lens according to the object lens characteristics.
It is another object of the present invention to provide a spatial modulation unit that can efficiently utilize the luminous flux that has passed through the exit pupil of an object lens according to the object lens characteristics.
It is still another object of the present invention to provide a luminous flux deflection device that can efficiently utilize the luminous flux that has passed through the exit pupil of an object lens according to the object lens characteristics.
It is still another object of the present invention to provide a camera that can efficiently utilize the luminous flux that has passed through the exit pupil of an object lens according to the object lens characteristics.
It is still another object of the present invention to provide a focus control device that can efficiently utilize the luminous flux that has passed through the exit pupil of an object lens according to the object lens characteristics.
In order to achieve the above object, according to one aspect of the present invention, there is provided a focus detection device comprising: a focus detector; a deflector that is arranged between a lens and the focus detector and that deflects luminous flux guided from the lens to the focus detector, wherein the deflector enables a deflection characteristic of the luminous flux guided from the lens to the focus detector to be changed; and a controller for controlling the deflector on a basis of pupil information upon an exit pupil of the lens and for changing the deflection characteristic of the luminous flux guided from the lens to the focus detector.
In the device, the controller controls the deflector on a basis of the size, position and so on of the exit pupil of the lens and guides the luminous flux from the lens to the focus detector by appropriately deflecting the luminous flux.
The luminous flux to be guided to the focus detector can be selected by changing the state of deflection of the luminous flux by the deflector, and therefore, sensing in a wide range can be executed regardless of the size, position and so on of the exit pupil of the lens.
For example, even a lens having a small aperture size, of which the f value has been too large to be detected with a fixed optical path as in the conventional case, can be detected if the luminous flux within the full span of its exit pupil is guided to the focus detector. In contrast to this, in the case of a lens having a large aperture size, the detection accuracy can be improved by utilizing the luminous flux located outside the conventional fixed optical path, i.e., in an area apart from the optical axis and the luminous flux in an area wider than the conventional area.
It is assumed that two image sensors are arranged while being displaced in the direction of optical axis of the imaging lens and the focal position is estimated without moving the focus lens by predicting (extrapolating or interpolating) a difference between two contrast output values. If the quantity of defocus is great, then the focal position can be found more easily as the distance between the two sensor positions in the direction in which the sensors are arranged (focus displacement quantity) is greater. Conversely, if the quantity of defocus is small, then it is preferred to set small the distance between the two sensor positions in the direction in which the sensors are arranged (focus displacement quantity) in order to increase the focus detection accuracy. If the focus detection device having the above-mentioned construction is employed, then the accuracy of the final focal position determination (AF completion) can be increased by largely separating the focal positions of the two sensors apart from each other by the deflector when the defocus is large and reducing the distance in the optical axis direction as the focusing is becoming advanced. Even when the defocus is large, rapid AF can be achieved.
Therefore, the luminous flux that has passed through the exit pupil can be efficiently utilized according to the object lens.
In order to achieve the above object, according to another aspect of the present invention, there is provided a spatial modulation unit comprising: a deflector having a plurality of deflection cells arranged in one of a concentric oval shape or a concentric quasi-oval shape; and a controller for electromagnetically controlling the deflection cells of the deflector so as to change a focal position of luminous flux incident on the deflection cells of the deflector.
In order to achieve the above object, according to still another aspect of the present invention, there is provided a luminous flux deflection device comprising: a deflector that is arranged between a lens and a detector and that deflects luminous flux guided from the lens to the detector, wherein the deflector enables a deflection characteristic of the luminous flux guided from the lens to the detector to be changed; and a controller for controlling the deflector on a basis of pupil information upon an exit pupil of the lens and for changing the deflection characteristic of the luminous flux guided from the lens to the detector.
In order to achieve the above object, according to still another aspect of the present invention, there is provided a camera comprising: a focus detector; a deflector that is arranged between a lens and the focus detector and that deflects luminous flux guided from the lens to the focus detector, wherein the deflector enables a deflection characteristic of the luminous flux guided from the lens to the focus detector to be changed; and a controller for controlling the deflector on a basis of pupil information upon an exit pupil of the lens and for changing the deflection characteristic of the luminous flux guided from the lens to the focus detector.
In order to achieve the above object, according to still another aspect of the present invention, there is provided a focus control device comprising: a lens for transmitting subject light; a driver for driving the lens;
an image sensor for detecting at least a part of the subject light transmitted through the lens; a spatial modulation unit that is arranged between the lens and the image sensor and that is able to electromagnetically change a focal position; a contrast type of focus detector for detecting a focal position on a basis of sharpness of an image detected by the image sensor; and a control unit for controlling the spatial modulation unit and the contrast type of focus detector so that the spatial modulation unit can change the focal position until the contrast type of focus detector detects the focal position and then for controlling the driver so as to drive the lens on a basis of the focal position detected by the contrast type of focus detector, wherein a change by the spatial modulation unit of the focal position is one of a continuous change and a change made step by step.
In order to achieve the above object, according to still another aspect of the present invention, there is provided a focus control device comprising: a lens for transmitting subject light; a driver for driving the lens; an image sensor for detecting at least a part of the subject light transmitted through the lens; a spatial modulation unit that is arranged between the lens and the image sensor and that is able to electromagnetically change a focal position; a phase difference type of focus detector for detecting a focal position by using an image detected by the image sensor; and a control unit for controlling the spatial modulation unit and the phase difference type of focus detector so that the phase difference type of focus detector can detect the focal position after the spatial modulation unit changes the focal position on a basis of pupil information upon an exit pupil of the lens and then for controlling the driver so as to drive the lens on a basis of the focal position detected by the phase difference type of focus detector.